Drying oils treated by irradiation as coatings for biobased films

Biobased films are potential food packaging materials. However, their performance with respect to water and gas barrier properties is inferior to current packaging products on market. Drying oils are promising as film coatings to improve water barrier properties of protein-based films. Drying oils undergo autoxidation after a period exposure to air to yield high molecular weight polymers that form water resistant coatings. However, curing of drying oils at ambient conditions is very slow and technologies for fast curing are needed. Furthermore, curing technologies must be safe for food related applications. Gamma radiation is known to promote the formation of free radicals which is an essential step in oil autoxidation. Thus, the objectives of this work were: (1) to investigate the effect of oil pre-treatment with gamma radiation on the drying rate of linseed and tung oils, (2) to investigate the effect of infrared radiation as curing treatment on the drying rate of linseed and tung oils, and (3) to investigate the structure of cured linseed and tung oil films. FTIR spectroscopy was used to monitor the linseed and tung oils drying process. The surface morphology of polymerized films was investigated by SEM. Experimental results indicated that oil pre-treatment with gamma radiation increased the drying rate of linseed and tung oils. Also, the drying rate of linseed and tung oils was increased when oils were cured under infrared radiation. Linseed and tung oil cured films presented clear morphological differences between them. Morphological features in cured linseed oil films corresponded with ductile properties while tung oil films were found to be hard and brittle. Main conclusions from this study are that oil pre-treatments with gamma radiation and curing under infrared are potential methods to increase the drying rate of linseed and tung oils. The study also evidenced that the choice of drying oil has important implications on the properties of cured films.